Method of operating a lithium-based battery pack for a hand held power tool

ABSTRACT

A method for conducting an operation including a power tool battery pack. The battery pack can include a housing, a first cell supported by the housing and having a voltage, and a second cell supported by the housing and having a voltage. The battery pack also can be connectable to a power tool and be operable to supply power to operate the power tool. The method can include discharging one of the first cell and the second cell until the voltage of the one of the first cell and the second cell is substantially equal to the voltage of the other of the first cell and the second cell.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/792,665, filed Feb. 17, 2020, now U.S. Pat. No. 10,886,762, which isa continuation of U.S. patent application Ser. No. 16/285,414, filedFeb. 26, 2019, now U.S. Pat. No. 10,566,810, which is a continuation ofU.S. patent application Ser. No. 15/948,311, filed Apr. 9, 2018, nowU.S. Pat. No. 10,218,194, which is a continuation of U.S. patentapplication Ser. No. 15/614,191, filed Jun. 5, 2017, now U.S. Pat. No.9,941,718, which is a continuation of U.S. patent application Ser. No.15/193,294, filed Jun. 27, 2016, now U.S. Pat. No. 9,673,648, which is acontinuation of U.S. patent application Ser. No. 14/695,614, filed Apr.24, 2015, now U.S. Pat. No. 9,379,569, which is a continuation of U.S.patent application Ser. No. 13/871,172, filed Apr. 26, 2013, now U.S.Pat. No. 9,018,903, which is a continuation of U.S. patent applicationSer. No. 13/568,265, filed on Aug. 7, 2012, now U.S. Pat. No. 8,450,971,which is a continuation of U.S. patent application Ser. No. 13/109,116,filed on May 17, 2011, now U.S. Pat. No. 8,269,459, which is acontinuation of U.S. patent application Ser. No. 12/331,088, filed onDec. 9, 2008, now U.S. Pat. No. 7,944,173, which is a continuation ofU.S. patent application Ser. No. 11/780,829, filed on Jul. 20, 2007, nowU.S. Pat. No. 7,554,290, which is a continuation of U.S. patentapplication Ser. No. 10/721,800, filed on Nov. 24, 2003, now U.S. Pat.No. 7,253,585, the entire contents of all of which are herebyincorporated by reference. U.S. patent application Ser. No. 10/721,800claims the benefit of U.S. Provisional Patent Application No.60/428,356, filed on Nov. 22, 2002; U.S. Provisional Patent ApplicationNo. 60/428,358, filed on Nov. 22, 2002; U.S. Provisional PatentApplication No. 60/428,450, filed on Nov. 22, 2002; U.S. ProvisionalPatent Application No. 60/428,452, filed on Nov. 22, 2002; U.S.Provisional Patent Application No. 60/440,692, filed on Jan. 17, 2003;U.S. Provisional Patent Application No. 60/440,693, filed on Jan. 17,2003; U.S. Provisional Patent Application No. 60/523,712, filed on Nov.19, 2003; and U.S. Provisional Patent Application No. 60/523,716, filedon Nov. 19, 2003, the entire contents of all of which are herebyincorporated by reference. This application also hereby incorporates byreference the entire contents of U.S. patent application Ser. No.10/720,027, filed on Nov. 20, 2003, now U.S. Pat. No. 7,157,882, andU.S. patent application Ser. No. 10/719,680, filed on Nov. 20, 2003, nowU.S. Pat. No. 7,176,654.

FIELD OF THE INVENTION

The present invention generally relates to battery packs and, moreparticularly, to power tool battery packs.

BACKGROUND OF THE INVENTION

Typically, electrical equipment, such as, for example, a cordless powertool, is powered by a rechargeable battery. The battery may beperiodically charged in a compatible battery charger.

SUMMARY OF THE INVENTION

FIGS. 36-38 illustrate an existing battery pack 230. The existingbattery pack 230 includes a housing 242 and at least one rechargeablebattery cell 246 (shown in FIGS. 39-40 ) supported by the housing 242.In the illustrated construction, the existing battery pack 230 is an 18Vbattery pack including (see FIGS. 39-40 ) fifteen approximately 1.2Vbattery cells 246 connected in series. The battery cells 246 are arechargeable battery cell chemistry type, such as, for example, NiCd orNiMH.

As shown in FIGS. 39-40 , in the existing battery pack 230, each batterycell 246 is generally cylindrical and extends along a cell axis 250parallel to the cylindrical outer cell wall. In the existing batterypack 230, the cell axes 250 are parallel to one another. Also, in theexisting battery pack 230, each battery cell 246 has a cell length 252which is about two times the cell diameter 254. In the illustratedconstruction, each battery cell 246 has a length of about forty-sixmillimeters (46 mm) and a diameter of about twenty-three millimeters (23mm).

The existing battery pack 230 is connectable to (see FIG. 12 ) a batterycharger 38, and the battery charger 38 is operable to charge theexisting battery pack 230. The existing battery pack 230 is connectableto electrical equipment, such as, for example, a power tool 34 (shown inFIG. 11A), to power the power tool 34. As shown in FIGS. 36-38 , thehousing 242 provides a support portion 250 for supporting the existingbattery pack 230 on an electrical device. In the illustratedconstruction, the support portion 250 provides (see FIG. 36 ) a C-shapedcross section which is connectable to a complementary T-shaped crosssection support portion on the electrical device (the support portion onthe power tool 34 (shown in FIG. 11B) and/or the battery support portionon the battery charger 38 (shown in FIG. 12 )).

The existing battery pack 230 includes (see FIGS. 36-37 and 39-40 ) aterminal assembly 286 operable to electrically connect battery cells 246to a circuit in the electrical device. The terminal assembly 286includes a positive battery terminal 298, a ground terminal 302, and asense terminal 306. As illustrated in FIGS. 39-40 , the terminals 298and 302 are connected to the opposite ends of the cell or series ofcells 246. The sense terminal 306 is connected to (see FIG. 40 ) anelectrical component 314 which is connected in the circuit of theexisting battery pack 230. In the illustrated construction, theelectrical component 314 is a temperature-sensing device or thermistorto communicate the temperature of the existing battery pack 230 and/orof the battery cells 246.

The present invention provides a battery pack which substantiallyalleviates one or more independent problems with the above-described andother existing battery packs. In some aspects and in some constructions,the present invention provides a battery pack including a two cellswhich are positioned in non-parallel relation to each other. In someaspects, the two cells are positioned in normal relation to each other.

More particularly, in some aspects and in some constructions, thepresent invention provides a battery pack including a housing, a firstcell extending along a first cell axis, and a second cell extendingalong a second cell axis, the first cell and the second cell beingsupported by the housing in an orientation in which the first cell axisis non-parallel to the second cell axis. In some aspects and in someconstructions, the first cell axis is normal to the second cell axis.

Also, in some aspects and in some constructions, the present inventionprovides a method of assembling a battery pack, the method including theacts of providing a battery pack housing, supporting a first cell withthe housing, and supporting a second cell with the housing innon-parallel relation to the first cell. In some aspects, the act ofsupporting the second cell includes supporting the second cell in normalrelation to the first cell.

In addition, in some aspects and in some constructions, the presentinvention provides a battery pack including a plurality of cells, asensor for sensing the voltage of a first group of the plurality ofcells, a sensor for sensing the voltage of a second group of theplurality of cells, and a controller for comparing the voltage of thefirst group to the voltage of the second group to determine if one ofthe plurality of cells is at or below a voltage.

Further, in some aspects and in some constructions, the presentinvention provides a method of determining a voltage of a cell of abattery pack, the battery pack including a plurality of cells, themethod including the acts of sensing the voltage of a first group of theplurality of cells, sensing the voltage of a second group of theplurality of cells, and comparing the voltage of the first group to thevoltage of the second group to determine if one of the plurality ofcells is at or below a voltage.

Also, in some aspects and in some constructions, the present inventionprovides a battery pack including a housing, a cell supported by thehousing, a FET connected to the cell, and a heat sink in heat-transferrelationship with the FET.

In addition, in some aspects and in some constructions, the presentinvention provides a method of assembling a battery pack, the methodincluding the acts of providing a housing, supporting a cell with thehousing, supporting a FET with the housing, connecting the FET to thecell, and supporting a heat sink in heat-transfer relationship with theFET.

In one embodiment, the invention provides a rechargeable battery packfor powering a high current draw hand held power tool. The battery packincludes a housing and a plurality of battery cells. The housing isconnectable to and supportable by the hand held power tool. Theplurality of battery cells are supported by the housing. The batterycells are capable of producing an average battery pack discharge currentgreater than or equal to approximately 20 amps and have a lithium-basedchemistry.

Independent features and independent advantages of the invention willbecome apparent to those skilled in the art upon review of the detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of a battery.

FIG. 2 is a top rear perspective view of a battery pack shown in FIG. 1.

FIG. 3 is a bottom rear perspective view of the battery pack shown inFIG. 1 .

FIG. 4 is a top view of the battery pack shown in FIG. 1 .

FIG. 5 is a bottom view of the battery pack shown in FIG. 1 .

FIG. 6 is a front view of the battery pack shown in FIG. 1 .

FIG. 7 is a rear view of the battery pack shown in FIG. 1 .

FIG. 8 is a right side view of the battery pack shown in FIG. 1 .

FIG. 9 is a left side view of the battery pack shown in FIG. 1 .

FIG. 10 is a bottom view of an alternate construction of a battery packembodying aspects of the present invention.

FIG. 11A is a perspective view of an electrical device, such as a powertool, for use with the battery pack shown in FIG. 1 .

FIG. 11B is a perspective view of the support portion of the power toolshown in FIG. 11A.

FIG. 12 is a perspective view of an electrical device, such as a batterycharger, for use with the battery pack shown in FIG. 1 .

FIG. 13 is a perspective view of a portion of the battery pack shown inFIG. 1 and illustrating the battery cells and the battery terminalassembly.

FIG. 14 is a top view of the battery cells and the battery terminalassembly shown in FIG. 13 .

FIG. 15 is a bottom view of the battery cells and the battery terminalassembly shown in FIG. 13 .

FIG. 16 is a front view of the battery cells and the battery terminalassembly shown in FIG. 13 .

FIG. 17 is a rear view of the battery cells and the battery terminalassembly shown in FIG. 13 .

FIG. 18 is a right side view of the battery cells and the batteryterminal assembly shown in FIG. 13 .

FIG. 19 is a left side view of the battery cells and the batteryterminal assembly shown in FIG. 13 .

FIG. 20 is a schematic diagram of components of a battery pack, such asthe battery pack shown in FIG. 1 .

FIG. 21 is another schematic diagram of components of a battery pack.

FIG. 22 is yet another schematic diagram of components of a batterypack.

FIG. 23 is still another schematic diagram of components of a batterypack.

FIG. 24 is a perspective view of a portion of the battery pack shown inFIG. 1 with portions removed.

FIG. 25 is a perspective view of a portion of the battery pack shown inFIG. 1 with portions removed.

FIG. 26 is a perspective view of a portion of the battery pack shown inFIG. 1 with portions removed.

FIG. 27 is a top view of the portion of the battery pack shown in FIG.26 .

FIGS. 28A-28E illustrate views of portions of the battery pack shown inFIG. 26 .

FIG. 29 is an exploded perspective view of a portion of the battery packshown in FIG. 1 with portions removed.

FIG. 30 is a rear perspective view of a portion of the battery packshown in FIG. 1 with portions removed.

FIG. 31 is another rear perspective view of the portion of the batterypack shown in FIG. 30 .

FIG. 32 is an exploded perspective view of a portion of the battery packshown in FIG. 1 with portions removed.

FIG. 33 is a perspective view of the portion of the battery pack shownin FIG. 32 .

FIG. 34 is an enlarged perspective view of a portion of the battery packshown in FIG. 33 .

FIGS. 35A-35C illustrate views of portions of the battery pack shown inFIG. 1 with portions removed.

FIG. 36 is a rear perspective view of an existing battery pack.

FIG. 37 is a front perspective view of the battery pack shown in FIG. 36.

FIG. 38 is a left side view of the battery pack shown in FIG. 36 .

FIG. 39 is a perspective view of a portion of the battery pack shown inFIG. 36 and illustrating the battery cells and the battery terminalassembly.

FIG. 40 is a right side view of the battery cells and the batteryterminal assembly shown in FIG. 39 .

FIG. 41 is a front perspective view of another battery pack.

FIG. 42 is right side view of the battery pack shown in FIG. 41 .

FIG. 43 is a left side view of a battery pack shown in FIG. 41 .

FIG. 44 is a top view of a battery pack shown in FIG. 41 .

FIG. 45 is a bottom rear perspective view of the battery pack shown inFIG. 41 .

FIG. 46 is a front view of the battery pack shown in FIG. 41 .

FIG. 47 is a rear view of the battery pack shown in FIG. 41 .

FIG. 48 is a front perspective view of a further battery pack.

FIG. 49 is right side view of the battery pack shown in FIG. 48 .

FIG. 50 is a left side view of a battery pack shown in FIG. 48 .

FIG. 51 is a top view of a battery pack shown in FIG. 48 .

FIG. 52 is a bottom rear perspective view of the battery pack shown inFIG. 48 .

FIG. 53 is a front view of the battery pack shown in FIG. 48 .

FIG. 54 is a rear view of the battery pack shown in FIG. 481 .

FIG. 55 is a perspective view of a battery pack in use with a firstelectrical device, such as a power tool.

FIG. 56 is a perspective view of a battery pack in use with a secondelectrical device, such as a power tool.

FIG. 57 is a perspective view of a portion of a battery pack andillustrating the battery cells.

FIG. 58 is a perspective view of a portion of a battery pack andillustrating the battery cells, terminals, end caps and circuitry.

FIG. 59 is a rear perspective view of the portion of the battery packshown in FIG. 58 .

FIG. 60 is a right side view of the portion of the battery pack shown inFIG. 58 .

FIG. 61 is a left side view of the portion of the battery pack shown inFIG. 58 .

FIG. 62 is a front view of the portion of the battery pack shown in FIG.58 .

FIG. 63 is a rear view of the portion of the battery pack shown in FIG.58 .

FIG. 64 is a top view of the portion of the battery pack shown in FIG.58 .

FIG. 65 is a perspective view of a portion of a battery pack andillustrating the end caps.

FIG. 66 is a partial side perspective view of a portion of the housingof a battery pack.

FIG. 67 is a partial front perspective view of the portion of thehousing shown in FIG. 66 .

FIGS. 68-69 are still further schematic diagrams of components of abattery pack.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein are for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items.

DETAILED DESCRIPTION

A battery pack 30 embodying aspects of the invention is illustrated inFIGS. 1-9 . The battery pack 30 can be connectable to electricalequipment, such as, for example, a cordless power tool 34 (shown in FIG.11A) to selectively power the power tool 34. The battery pack 30 can beremovable from the power tool 34 and can be rechargeable by a batterycharger 38 (shown in FIG. 8 ).

As shown in FIGS. 1-9 , the battery pack 30 includes a housing 42 and atleast one rechargeable battery cell 46 (shown in FIGS. 13-19 ) supportedby the housing 42. In the illustrated construction, the battery pack 30can be a 21V battery pack including five approximately 4.2V batterycells 46 a, 46 b, 46 c, 46 d and 46 e connected in series. In otherconstructions (not shown), the battery pack 30 may have another nominalbattery voltage, such as, for example, 9.6V, 12V, 14.4V, 24V, etc., topower the electrical equipment and be charged by the battery charger 38.It should be understood that, in other constructions (not shown), thebattery cells 46 may have a different nominal cell voltage and/or may beconnected in another configuration, such as, for example, in parallel orin a parallel/series combination.

The battery cells 46 may be any rechargeable battery cell chemistrytype, such as, for example, nickel cadmium (NiCd), nickel-metal hydride(NiMH), Lithium (Li), Lithium-ion (Li-ion), other Lithium-basedchemistry, other rechargeable battery cell chemistry, etc. In theillustrated construction, the battery cells 46 can be lithium-ion(Li-ion) battery cells. For example, the battery cells 46 can have achemistry of Lithium-Cobalt (Li—Co), Lithium—Manganese (Li—Mn) Spinel,Li—Mn Nickel, or the like.

As shown in FIGS. 13-20 , in the battery pack 30, each battery cell 46a-46 e can be generally cylindrical and can extend along a cell axis 50a-50 e parallel to the cylindrical outer cell wall. Also, in the batterypack 30, each battery cell 46 can have a cell length 52 which is morethan two times and almost three times the cell diameter 54. In theillustrated construction and in some aspects, each battery cell 46 canhave a diameter of about twenty-six millimeters (26 mm) and a length ofat least about sixty millimeters (60 mm). In some constructions, eachbattery cell 46 can have a length of about sixty-five millimeters (65mm). In some constructions, each battery cell 46 can have a length ofabout seventy millimeters (70 mm).

The battery cells 46 are arranged in a first set 56 of battery cells 46a, 46 b and 46 c and a second set 58 of battery cells 46 d and 46 e. Inthe first set 56, the cell axes 50 a, 50 b and 50 c are parallel to oneanother. In the second set 58, the cell axes 50 d and 50 e are parallelto each other. However, the sets 56 and 58 are arranged so that thebattery cells 46 a, 46 b and 46 c are non-parallel to the battery cells46 d and 46 e. In the illustrated construction, for example, the batterycells 46 a, 46 b and 46 c can be normal to the battery cells 46 d and 46e.

The battery cells 46 are arranged to reduce the heat transfer betweenthe battery cells 46 and to improve the collection and removal of heatfrom the battery cells 46. In this manner, the battery cells 46 may beable to be maintained in an appropriate temperature operating range forlonger durations of use. The battery cells 46 are also arranged toprovide an efficient use of space and to maintain a relatively smallpack size.

As shown in FIGS. 1-4 and 7 , the housing 42 can provide a supportportion 60 for supporting the battery pack 30 on an electrical device,such as the power tool 34 or the battery charger 38. In the illustratedconstruction, the support portion 60 provides a C-shaped cross section(see FIG. 7 ) which is connectable to a complementary T-shaped shapedcross section support portion on the electrical device.

The battery pack 30 also can include (see FIGS. 1-4, 8-9, 21, 24-25 and30-38 ) a locking assembly 74 operable to lock the battery pack 30 to anelectrical device, such as, for example, to the power tool 34 and/or toa battery charger. The locking assembly 34 includes locking members 78which are movable between a locked position, in which the lockingmembers 78 engage a corresponding locking member on the electricaldevice to lock the battery pack 30 to the electrical device, and anunlocked position. The locking assembly 74 also includes actuators 82for moving the locking members 78 between the locked position and theunlocked position. The actuators 82 have a large surface for engagementby an operator to provide improved ease of unlocking the lockingassembly 74. Also, the actuators 82 are supported to reduce the grippingforce required to unlock the locking assembly 74.

As shown in FIGS. 30-38 , biasing members 83 bias the locking members 78toward the locked position. In the illustrated construction, eachbiasing members 83 is a leaf spring positioned between the actuator 82and the housing 42 to bias the locking member 78 to the locked position.

Each biasing member 83 is fixed between the actuator 82 and the housing42 and operates to retain the actuator 82 (and the locking member 78) ina position and to limit unwanted movement of the actuator 82 (and thelocking member 78) relative to the housing 42. Specifically, the biasingmember 83 limits movement of the actuator 82 (and of the locking member78) in a direction perpendicular to the direction of movement betweenthe locked position and the unlocked position (i.e., upwardly in thecross-sectional views of FIG. 35 ) to prevent the actuator 82 and/or thelocking member 78 from binding on the housing 42 or from being preventedto move in the desired manner to operate the locking assembly 74.

As shown in FIGS. 32 and 35 , the biasing member 83 includes a housingleg 84 engaging the housing 42 to force the biasing member 83 downwardly(in the left cross-sectional view of FIG. 35 ). The biasing member 83also includes (see the right cross-sectional view of FIG. 35 ) anactuator leg 85 engaging the actuator 83 to draw and retain the actuator82 (and the locking member 78) in the correct downward position (in thecross-sectional views of FIG. 35 ) during operation of the lockingassembly 74 and of the battery pack 30.

The battery pack 30 includes (see FIGS. 1-5, 7, 13-14 and 17-20 ) aterminal assembly 86 operable to electrically connect the battery cells46 to a circuit in the electrical device. The terminal assembly 86includes (see FIGS. 1-3 ) a positive battery terminal 98, a groundterminal 102, and a sense terminal 106. As schematically illustrated inFIG. 20 , the terminals 98 and 102 are connected to the opposite ends ofthe cell or series of cells 46.

The sense terminal 106 can be connected to one or more electricalcomponents, such as an identification component (i.e., a resistor) tocommunicate the identification of a characteristic of the battery pack30, such as, for example, the chemistry of the battery cells 46, thenominal voltage of the battery pack 30, etc., or a temperature-sensingdevice or thermistor to communicate the temperature of the battery pack30 and/or of the battery cell(s) 46. It should be understood that, inother constructions (not shown), the electrical components may be othertypes of electrical components and may communicate other characteristicsor information about the battery pack 30 and/or of the battery cell(s)46. It should also be understood that “communication” and “communicate”,as used with respect to the electrical components, may also encompassthe electrical components having or being in a condition or state whichis sensed by a sensor or device capable of determining the condition orstate of the electrical components.

In some constructions and in some aspects, the sense terminal 106 can beconnected to a circuit 430, as shown in FIGS. 21-23 and 68-69 . Thecircuit 430 can be electrically connected to one or more battery cells46, and can be electrically connected to one or more battery terminalsof the terminal block 86. In some constructions, the circuit 430 caninclude components to enhance the performance of the battery pack 30. Insome constructions, the circuit 430 can include components to monitorbattery characteristics, to provide voltage detection, to store batterycharacteristics, to display battery characteristics, to inform a user ofcertain battery characteristics, to suspend current within the battery50, to detect temperature of the battery pack 30, battery cells 46, andthe like, to transfer heat from and/or within the battery 30, and toprovide balancing methods when an imbalance is detected within one ormore battery cells 46. In some constructions and in some aspects, thecircuit 430 includes a voltage detection circuit, a boosting circuit, astate of charge indicator, and the like. In some constructions, thecircuit 430 can be coupled to a print circuit board (PCB) 145. In otherconstructions, the circuit 430 can be coupled to a flexible circuit 445,as discussed below. In some constructions, the flexible circuit 445 canwrap around one or more cells 46 or wrap around the interior of thehousing 42, as discussed below.

In some constructions, the circuit 130 can also include a microprocessor430. The microprocessor 430 can monitoring various battery packparameters (e.g., battery pack present state of charge, battery cellpresent state of charge, battery pack temperature, battery celltemperature, and the like), can store various battery pack parametersand characteristics (including battery pack nominal voltage, chemistry,and the like, in addition to the parameters), can control variouselectrical components within the circuit 130, and can conductcommunication with other electrical devices, such as, for example, apower tool, a battery charger, and the like. In some constructions, themicroprocessor 430 can monitor each battery cell's present state ofcharge and can identify when an imbalance occurs (e.g., the presentstate of charge for a battery cell exceeds the average cell state ofcharge by a certain amount or drops below the average cell state ofcharge by a certain amount).

In some constructions and in some aspects, the circuit 430 can include avoltage detection circuit 459. In some constructions, the voltagedetection circuit 459 can include a plurality of resistors 460 formingresistor divider networks. As shown in the illustrated construction, theplurality of resistors 460 can include resistors 460 a-d. The pluralityof resistors 460 can be electrically connected to one or more batterycells 46 a-e and to a plurality of transistors 465. In the illustratedconstruction, the plurality of transistors 465 can include transistors465 a-d. In some constructions, the number of resistors included in theplurality of resistors 460 can equal the number of transistors includedin the plurality of transistors 465.

In some constructions, voltage characteristics of the battery pack 30and/or of the battery cells 46 can be read by the microprocessor 440through the plurality of resistors 460 when the microprocessor 440 is inthe active mode. In some constructions, the microprocessor 440 caninitiate a voltage-read event by turning off transistor(s) 470 (i.e.,transistor 470 becomes non-conducting). When the transistor(s) 470 isnon-conducting, the transistors 265 a-d become conducting and voltagemeasurements regarding the battery pack 30 and/or battery cells 46 canbe made by the microprocessor 440. Including the plurality oftransistors 465 in the battery pack 30 can reduce the parasitic currentdraw from the battery pack 30, because the transistors 465 are onlyconducting periodically.

In some constructions, the microprocessor 440 can monitor the voltage ofeach battery cell 46 and balance the cell 46 if an imbalance occurs. Aspreviously discussed, the battery pack 30 can include the plurality ofresistors 460 for providing voltage measurements of the battery cells46. The plurality of resistors 460 are arranged such that themicroprocessor 440 can measure the voltage of each battery cells 46 a-eapproximately at the same time. In some constructions, themicroprocessor 440 detects an imbalance within the battery pack 30 whenone or more cells 46 reach approximately 1 V.

In some constructions and in some aspects, the battery pack 30 mayre-balance the cells 46 when an imbalance has been detected via abalancing circuit 459. In some constructions, the battery pack 30re-balance the battery cells 46 when the battery pack 30 is in adischarging operation or act or when the battery pack 30 is notproviding a discharge current or receiving a charge current. In someconstructions, the balancing circuit 459 can include the plurality ofresistors 460 and the plurality of transistors 465. In someconstructions, the microprocessor 440 disables the battery 30 (e.g.interrupts battery operation, prevents battery operation, etc.) via theswitch 180 when a balanced ratio R between cells 46 is no longerincluded within an acceptable range. After the battery pack 30 isdisabled, the microprocessor 440 determines which cell(s) 46 isimbalanced (the “low voltage cell”).

In some constructions, the microprocessor 440 activates or turns on therespective transistors, such as, for example, transistors 465 a-d, thatare electrically connected to those cells 46 that are not low in presentstate of charge (i.e., cells having a higher present state of chargethan the low voltage cell). The microprocessor 440 begins a controlleddischarge of the high present state of charge cells 46. For example, themicroprocessor will control the small discharge current that will flowfrom the balanced cells 46 through the respective transistors. Themicroprocessor 440 will continue to make voltage measurements of thecells 46 throughout the controlled discharging process. Themicroprocessor 440 will end the controlled discharge process when thepresent state of charge of the higher state of charge cells 46 isreduced to be approximately equal to the previously low voltage cell.

Components of the circuit 430 and of the battery pack 30, such as, forexample, a FET 480, a heat sink 485, a thermistor 450, a fuel gauge 170(including one or more light-emitting diodes 470 a-d), a push-button 460for activating the fuel gauge 470, a microprocessor 440, and the like,are illustrated in more detail in FIGS. 20-29 . For some constructionsand for some aspects, these and other additional independent featuresand structure of the battery pack 30 and other operations of the batterypack 30 are described in more detail in U.S. patent application Ser. No.10/720,027, filed Nov. 20, 2003, now U.S. Pat. No. 7,157,882.

As shown in FIG. 8 , the battery charger 38 is connectable to thebattery pack 30 and is operable to charge the battery pack 30. Thebattery charger 38 includes a charger housing 122 providing a supportportion 124, on which the battery pack 30 is supported, and a chargingcircuit 126 (schematically illustrated in FIG. 12 ) is supported by thehousing 122 and connectable to a power source (not shown). The chargingcircuit 126 is connectable by a charger terminal assembly 128 to theterminal assembly 86 of the battery pack 30 and is operable to transferpower to the battery pack 30 to charge the battery cell(s) 46.

In some constructions and in some aspects, the charging circuit 126operates to charge the battery pack 30 in a manner similar to thatdescribed in U.S. Pat. No. 6,456,035, issued on Sep. 24, 2002, and U.S.Pat. No. 6,222,343, issued on Apr. 24, 2001, which are herebyincorporated by reference.

For some constructions and for some aspects, additional independentfeatures, structure and operation of the battery charger 38 aredescribed in more detail in U.S. patent application Ser. No. 10/720,027,filed Nov. 20, 2003, now U.S. Pat. No. 7,157,882, and U.S. patentapplication Ser. No. 10/719,680, filed Nov. 20, 2003, now U.S. Pat. No.7,176,654.

The battery pack 30 is connectable to electrical equipment, such as, forexample, the power tool 34 (shown in FIG. 11A), to power the power tool34. The power tool 34 includes a housing 182 supporting an electricmotor 184 (schematically illustrated) which is electrically connected tothe battery pack 30 by (see FIG. 11B) a power tool terminal assembly 186so that the motor 184 is selectively powered by the battery pack 30. Thehousing 182 provides (see FIG. 11B) a support portion 186 on which thebattery pack 30 is supported. The support portion 186 has a generallyT-shaped cross section which is complementary to the C-shaped crosssection of the support portion 60 of the battery pack 30. The supportportion 186 also defines locking recesses 188 (one shown) in which thelocking members 78 are engageable to lock the battery pack 30 to thepower tool 34.

An alternative construction of a battery pack 30A embodying aspects ofthe invention is illustrated in FIG. 10 . Common elements are identifiedby the same reference number “A”.

As stated previously, the battery pack 30 can include more or fewerbattery cells 46 than the embodiment shown, and can have a higher orlower nominal voltage than in the constructions shown and described. Forexample, one such construction of a battery pack 30B having a highernominal voltage is shown in FIGS. 41-47 . Common elements are identifiedby the same reference number “B”. A further construction of a batterypack 30C is shown in FIGS. 48-54 . Common elements are identified by thesame reference number “C”.

Unless specified otherwise, hereinafter, battery pack 30 can refer tothe various constructions of battery pack 30 (e.g., battery pack 30,battery pack 30A, battery pack 30B, and battery pack 30C). Also, unlessspecified otherwise, battery pack 30B can refer to both battery pack 30Band battery pack 30C.

In some constructions, the battery pack 30 can be configured fortransferring power to and receiving power from various electricaldevices, such as, for example, various power tools, battery chargers,and the like. In some constructions, such as, for example, theconstructions illustrated in FIGS. 55 and 56 , the battery pack 30 cansupply power to various power tools, such as, a driver drill 300, acircular saw 305, and the like. In some constructions, the battery pack30 can power various power tools (including a driver drill 300 and acircular saw 305) having high discharge current rates. For example, thebattery pack 30 can supply an average discharge current that is equal toor greater than approximately 20 A, and can have an ampere-hour capacityof approximately 3.0 A-h.

In some constructions, the battery pack 30, such as battery pack 30B,can include seven battery cells 346 a-g (shown in FIG. 57 ). In someconstructions, the battery cells 346 a-g can be similar to battery cells46 a-e included in the battery pack 30. In some constructions, thebattery cells 346 a-g can differ from battery cells 46 a-e in weight,size, nominal voltage, chemistry, and the like. For example, in oneconstruction, the battery cells 346 a-g can have a cell chemistry ofLi-ion, such as, for example, Li—Mn spinel, Li—Mn nickel, or Li—Co. Insome constructions, each cell 346 a-g can have a nominal voltage ofapproximately 3.6 V. In other constructions, each cell 346 a-g can havea nominal voltage of approximately 4 V, and in further constructions,each cell 346 a-g can have a nominal voltage of approximately 4.2 V. Insome constructions, the battery pack 30B can include seven battery cells346 a-g, and can have a nominal voltage of approximately 28 V. In otherconstructions, the battery pack 30B can include seven battery cells 346a-g, and can have a nominal voltage of approximately 25 V.

The battery cells 346 a-g can also be electrically connected in anysuitable manner, such as, for example, in a serial arrangement, aparallel arrangement, a partial serial arrangement (e.g., some of thebattery cells 346 a-g are connected in a serial arrangement), a partialparallel arrangement (e.g., some of the battery cells 346 a-g areconnected in a serial arrangement), a combination of a serial, parallel,partial serial or partial parallel arrangement. In one construction, thebattery cells 346 a-g are electrically connected in a serialarrangement. The battery cells 346 a-g can be electrically connected viaconductive straps 450. For example, a conductive strap 450 can connectthe negative end of the first battery cell 346 a to the positive end ofthe second battery cell 346 b. Also, another conductive strap 450 canconnected the negative end of the second battery cell 346 b to thepositive end of the third battery cell 346 c.

As shown in FIGS. 58-65 , the battery pack 30, such as battery pack 30B,can also include an end cap arrangement 505. In some constructions, theend cap arrangement can be used for spacing the battery cells 346. Theend cap arrangement 505 includes a first end cap 510 and a second endcap 515. The first and second end caps 510 and 515 can be connected by aconnecting portion 520. In some constructions, the connecting portion520 can be a hinge. In some constructions, the end cap arrangement 505does not include the connecting portion 520. Each end cap 510 and 515can partially define one or more cavities 530 (shown in FIG. 65 ). Theend of a battery cell 346 can be positioned within a cavity 530. In theillustrated construction, the first end cap 510 and the second end cap520 each include seven cavities 530 a-g for positioning seven batterycells 346 a-g, respectively.

In the illustrated construction, the first end cap 510 is positioned ata first end 490 (shown in FIG. 57 ) of the arrangement of battery cells346, and the second end cap 515 is positioned at the second end 495 ofthe arrangement of battery cells 346. As mentioned previously, each endof each battery cell 346 a-g can be positioned within the respectivecavities 530 a-g of the first and second end cap 510 and 515. Each endcap 510 and 515 can define the cavities 530 a-g in order to create gapsor spaces between the battery cells 346 when the battery cells 346 arepositioned within the cavities 530. This can allow for greater heatdissipation within the battery pack 30B by allowing air to circulatethrough the gaps and spaces between the cells 346.

In some constructions, the first end cap 510 and the second end cap 515can further define apertures 450. The apertures 450 can receive theconductive straps 450 for electrically connecting one battery cell 346to another battery cell 346.

In some constructions and in some aspects, the end cap arrangement 505can also include a flexible circuit 445. In some constructions, theflexible circuit 445 can be integral with either the first end cap 510,the second end cap 515, the connecting portion 520, or a combination. Inother constructions, the end cap arrangement 505 can define one or moreareas for supporting the flexible circuit. In further constructions, theflexible circuit 445 can be secured to the end cap arrangement 505. Asshown in the illustrated construction, the flexible circuit 445 canpartially wrap around the battery cells 346.

In the construction shown, the end cap arrangement 505 can include aconnector 560 for electrically connecting the flexible circuit 445 tothe PCB 145B. In this construction, the PCB 145B and the flexiblecircuit 445 each can each include a portion of the circuit 430 includedin the battery pack 30B.

In some constructions and in some aspects, the battery pack 30 caninclude cushion members or “bumpers” 640. As shown in FIGS. 66 and 67 ,the interior face 645 of the battery housing 42B can include one or morecushion members 640. In some constructions, the cushion members 640 canbe integral with the housing 42B. In other constructions, the cushionmembers 640 can be attached or secured to the interior face 645 of thehousing 42B. In further constructions, the cushion member 640 can beconnected to one or more battery cells 346 or to the end cap arrangement505 partially surrounding the battery cells 346. In some constructions,the cushion members 645 can absorb energy during impact and protect thebattery cells 346 during impact by limiting the amount of energytransferred to the cells 346. The cushion members 645 can include anythermoplastic rubber such as, for example, polypropylene RPT 100 FRHI(e.g., flame retardant-high impact).

One or more independent features or independent advantages of theinvention will be set forth in the claims.

We claim:
 1. A method of operating a battery pack, the methodcomprising: coupling a housing of the battery pack to a hand held powertool to support the battery pack on the hand held power tool, thebattery pack including a plurality of battery cells supported within thehousing, each of the plurality of battery cells having a lithium-basedchemistry, each of the plurality of battery cells having a cell widthand a cell length, the cell length being at least about two times thecell width, and first and second terminals for electrically connectingthe battery pack to the hand held power tool; and controlling, with acircuit, a discharge of the plurality of battery cells to produce adischarge current from the plurality of battery cells, an average of thedischarge current produced by the plurality of battery cells beinggreater than or equal to approximately 20 amps.
 2. The method of claim1, wherein each of the plurality of battery cells are cylindrical. 3.The method of claim 1, wherein the plurality of battery cells areconnected in a combined series-parallel configuration.
 4. The method ofclaim 1, wherein the cell length is between about two and about 2.7times the cell width.
 5. The method of claim 1, wherein the battery packhas an ampere-hour capacity of at least about 3.0 ampere-hours.
 6. Themethod of claim 1, wherein the battery pack has an ampere-hour capacityof up to about 3.0 ampere-hours.
 7. The method of claim 1, wherein thecell length is between about 60 mm and about 70 mm.
 8. The method ofclaim 1, wherein the cell length is about 65 mm.
 9. The method of claim1, wherein controlling the discharge of the plurality of battery cellsincludes controlling, with the circuit, a field-effect transistor(“FET”).
 10. The method of claim 9, wherein the FET is located withinthe housing.
 11. The method of claim 1, wherein the circuit includes amicroprocessor.